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This correction notice addresses errors and omissions in the article "Early Detection of Honeycombs in Concrete Pavement Using GPR" by Theresa McCabe, Ece Erdogmus, Antony Kodsy, and George Morcous. The correction includes the correct dimensions of the slabs tested, the correct embedded depths of the air voids, the correct identification of the ground-coupled antenna, the replacement of a word in a sentence, the correction of the vertical axis in a figure, the correction of the units in another figure, and a correction in the acknowledgements section. These corrections have been made to preserve the accuracy of the published version of the article. [Extracted from the article]

Structural parameters and inlet preswirl have great influences on the static and dynamic characteristics of honeycomb seals. In this paper, a multifrequency elliptical vortex dynamic model of a honeycomb seal was established by an unsteady dynamic grid technique. Based on verification of the numerical model, the effects of honeycomb cell size, axial length, and inlet preswirl on seal performance were investigated. Rotor–bearing–seal stability experiments were carried out to measure the logarithmic decrement rate of the rotor system under different rotational speeds, and the stability of the rotor system was further analyzed. The results showed that with increasing hole depth, leakage of the honeycomb seal increased initially due to the increasing airflow rate in response to vortex formation, and thereafter decreased, caused by the intense dissipation effect of turbulence. With increasing opposite-edge distance of core cell and decreasing axial length, the decreasing number of honeycomb cores on stator surfaces weakened the dissipation capacity of the turbulence, resulting in increases of leakage. Inlet preswirl had little effect on the leakage. However, it had a lower absolute value of tangential airflow excitation force and a lower effective damping coefficient under a higher inlet preswirl, indicating a lower dynamic characteristic of the honeycomb seal. Compared with other seals with different parameters, the honeycomb seal with structural parameters of B3H3L96 showed a higher effective damping coefficient under different inlet/outlet pressure ratios and different vortex frequencies and a higher logarithmic decrement rate under different rotational speeds, indicating a better stability of the rotor system. [ABSTRACT FROM AUTHOR]

Parameters of the honeycomb core, such as cell size and foil thickness, as well as the material of the core, influence the ballistic performance of honeycomb-core sandwich panels (HCSPs) in the case of hypervelocity impact (HVI) by orbital debris. Two predictive models that account for this influence have been developed in this study: a dedicated ballistic limit equation (BLE) and an artificial neural network (ANN) trained to predict the outcomes of HVI on HCSP. BLE fitting and ANN training was conducted using a database composed of entries resulting from physical and numerical experiments. The new ballistic limit equation was based on the Whipple shield BLE, in which the standoff distance between the facesheets was replaced by a function of the honeycomb cell size, foil thickness, and yield strength of the HC material. The BLE demonstrated excellent accuracy in predicting the ballistic limits of HCSP when tested against a new set of simulation data, with the discrepancy ranging from 1.13% to 5.58% only. The ANN was developed using MATLAB's version 2018b Deep Learning Toolbox framework and was trained utilizing the same HCSP HVI database as that employed for the BLE fitting. A comprehensive parametric study was conducted to optimize the ANN architecture, including such parameters as the activation function, the number of hidden layers, and the number of nodes per layer. The resulting ANN demonstrated a very good predictive accuracy when tested against a set of simulation data not previously used in the training of the network, with the discrepancy ranging from 0.67% to 7.27%. Both of the developed predictive models—the BLE and the ANN—can be recommended for use in the design of spacecraft orbital debris shielding involving honeycomb-core sandwich panels. [ABSTRACT FROM AUTHOR]

Making photovoltaic (PV) systems more energy efficient is a huge challenge toward their widespread adoption. Partial shading is one of the major contributors of power reduction in PV systems. The interconnection scheme of the modules, the pattern of partial shading, and the module setup area determine the extent of power reduction. Conventional literatures contain arrays set up in rectangular and square shapes following various topologies to neutralize the adverse effects of partial shadings. Therefore, new areas of research may include connection of solar modules in new shapes to form unevenly sized PV arrays. This paper includes PV modules configured in six types of novel triangular connections and compares their performances under shading conditions. These interconnection schemes are (1) triangular series-series (TSS), (2) triangular series-parallel (TSP), (3) triangular parallel-parallel (TPP), (4) triangular honeycomb (THC), (5) triangular bridge link (TBL), and (6) triangular total-cross-tied (TTCT). Each of the six configurations are compared to one another, taking into account their different performance parameters such as maximum power, fill factor, and power loss. The TSS configuration method is found to have a better performance edge over TSP, TBL, THC, and TTCT configurations for all the considered parameters. [ABSTRACT FROM AUTHOR]

In this study, glue-pressed engineered honeycomb bamboo (GPEHB) was prepared, and the dependence of the compressive properties of the produced GPEHB on the load–slenderness ratio, longitudinal strain–slenderness ratio, and ultimate strain–slenderness ratio was examined. The detailed failure modes were also investigated. The main failure modes of the short GPEHB specimens were squashing, crushing, and splitting, and the bearing capacity was mainly dependent on the compressive strength of the bamboo units. Buckling failure modes involving significant lateral deflection were observed for the long GPEHB specimens. With increasing slenderness ratio, the bearing capacities of the GPEHB specimens decreased significantly. The ultimate load of the GPEHB specimens decreased significantly as the slenderness ratio increased from 4 to 6 (GPEHB length increased from 736 to 1,104 mm). The ultimate deformation behaviors of the specimens were fit well by a quadratic function of the slenderness ratio. The GPEHB was also analyzed and modeled via finite element analysis (FEA). The experimental results, theoretical calculations, and FEA analysis results were compared. [ABSTRACT FROM AUTHOR]

The goal of this research is to evaluate whether it is possible and effective to detect honeycombing of concrete pavement using a ground-penetrating radar (GPR) during construction. The motivation is that identifying honeycombing of concrete during construction would help avoid the spread of consolidation problems in large pavement sections, which are costly and time consuming to repair. GPR has been used as a tool for concrete quality control and detection of delamination in reinforced concrete elements since the 1980s, but it has not been used for the early detection of relatively small air voids. In this project, first, preliminary field testing was conducted to determine the possibility of detecting honeycombs in existing concrete pavement. Then, air voids of different sizes, shapes, and depths were artificially created using spray-foam in several laboratory specimens and detected using a high-frequency GPR antenna at different times after concrete placement. Cores were extracted to validate GPR readings and determine the capability of this technique. Another field testing was conducted to evaluate the efficiency and economy of using GPR as a nondestructive quality control tool. Field and lab test results indicated that GPR could be efficiently used to detect air voids as small as 32 mm (1.25 in.) and as deep as 102 mm (4 in.) from the surface of the concrete pavement as early as the initial set of concrete. These findings suggest that GPR is an effective, efficient, and economic quality control tool for this application. [ABSTRACT FROM AUTHOR]

In the applications of composite honeycomb sandwich structures, they often are severely impacted, resulting in partial penetration or complete perforation. To study the mechanical response of composite honeycomb sandwich structures under high-velocity impact, an extended P-α model was developed to describe the equivalent property of honeycomb materials. Extended P-α model parameters were determined using analytical and experimental techniques. Based on the equivalent model, the impact response had good agreement between the experimental results and numerical simulation. By comparison with the detailed model in terms of ballistic limit, residual velocity, maximum displacement of the projectile, and contact time, the results from the equivalent model are not only reliable but also computationally efficient, because the equivalent model requires only 25% as much time as the detailed model under the same conditions. [ABSTRACT FROM AUTHOR]

The effective in-plane elastic moduli of different types of honeycomb cores with thick walls are studied using analytical and numerical approaches. Analytical equations derived in this paper take a proposed jointed rectangle into consideration. The analytical results under plane stress and plane strain conditions are also obtained. The effective in-plane elastic moduli are studied as a function of their own relative densities because of the different methods of describing the geometrical shapes of honeycomb cores. The results are quantitatively compared with the available experimental results in this paper. It indicates that the present model can better predict the elastic properties in x -direction but are less suitable in y -direction. The proposed jointed rectangle has significant effect at high relative density. Moreover, the effective in-plane modulus increases with the relative height of honeycomb cores because of the Poisson effect of the material, and the results under plane stress and plane strain conditions are the lower and upper bounds, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a spacecraft radiator formed in a honeycomb structure is designed to enhance the thermal performance while reducing its mass. Examples of design guidelines for radiator configurations, such as the distance between heat pipes, facesheet thickness, and honeycomb core density, are suggested. To derive the analytic solution of the governing equation, a linear approximation is used and the accuracies of the solutions are verified with a fourth-order finite-difference method. There exist optimal combinations of design parameters that minimize the radiator mass while maintaining its heat rejection capacity. The heat rejection rate that minimizes the mass per unit heat rejection and the pertinent radiator shape also is presented. The combinations of optimal design are different among the three surface treatments and their characteristics are investigated. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for the modal system identification of a large mechanical structure by combining results from simulations and physical measurements. Specifically, reconstruction of mode shapes was accomplished by comparing simulated and measured amplitude ratios generated using a Nyquist analysis. The methodology developed in this paper improves upon traditional techniques by allowing for statistically cross-referencing relatively few sensor measurements and a relatively simple simulation model. This methodology was used to identify three major modal frequencies and mode shapes of the main aluminum honeycomb sandwich panel gondola structure of the balloon-borne imaging testbed (BIT). BIT was a stratospheric ballooning project for astronomy that was launched on September 18, 2015, from Timmins, Ontario, Canada. Ensuring that structural vibrations do not adversely affect the pointing accuracy of the on-board telescope is crucial to the success of the project. This paper also highlights some of the advantages and drawbacks of the presented methodology and suggests improvements for future applications in balloon-borne experiments. [ABSTRACT FROM AUTHOR]

An analytical framework has been proposed to analyze the effect of random structural irregularity in honeycomb core for natural frequencies of sandwich panels. Closed-form formulas have been developed for the out-of-plane shear moduli of spatially irregular honeycombs following minimum potential energy theorem and minimum complementary energy theorem. Subsequently an analytical approach has been presented for free-vibration analysis of honeycomb core sandwich panels to quantify the effect of such irregularity following a probabilistic paradigm. Representative results have been furnished for natural frequencies corresponding to low vibration modes of a sandwich panel with high length-to-width ratio. The results suggest that spatially random irregularities in honeycomb core have considerable effect on the natural frequencies of sandwich panels. [ABSTRACT FROM AUTHOR]

Numerical simulation is often used in the design of aircraft structural components subjected to bird-strike loads. To verify the numerical method, a test of bird striking was performed on honeycomb-based sandwich panels made from 3003 aluminum honeycomb and 2024-T3 aluminum skin. The dynamic responses of displacement and strain on the rear skin of the sandwich panel during bird striking were measured using strain gauges and a laser sensor, respectively. A numerical model of bird striking was developed with a nonlinear, finite-element program. A coupling smooth particle hydrodynamics-finite-element analysis algorithm was used to simulate the interaction of the impacting contact between the bird and the target. The numerical simulation results were compared with the tests, and they are in good agreement, which validated the reasonableness of the numerical model established in the present paper. This shows the potential of using the FEM in simulating the dynamic response of aircraft structural components in bird-strike events. [ABSTRACT FROM AUTHOR]

This paper describes the experimental and analytical evaluation of an externally deployable composite honeycomb structure that is designed to attenuate impact energy during helicopter crashes. The concept, designated the deployable energy absorber (DEA), uses an expandable Kevlar honeycomb to dissipate kinetic energy through crushing. The DEA incorporates a unique flexible-hinge design that enables the honeycomb to be packaged and stowed efficiently until needed for deployment. Experimental evaluation of the DEA included dynamic crush tests of multicell components and vertical drop tests of a composite fuselage section retrofitted with DEA blocks onto multiterrain. Finite-element models of the test articles were developed and simulations were performed using the transient dynamic code LS-DYNA. In each simulation, the DEA was represented using shell elements assigned two different material properties: Mat 24, an isotropic piecewise linear plasticity model, and Mat 58, a continuum damage mechanics model used to represent laminated composite fabrics. DEA model development and test analysis comparisons are presented. [ABSTRACT FROM AUTHOR]

The National Aeronautics and Space Administration (NASA) has sponsored research to evaluate an externally deployable composite honeycomb designed to attenuate loads in the event of a helicopter crash. The concept, designated the deployable energy absorber (DEA), is an expandable Kevlar honeycomb. The DEA incorporates a flexible hinge that allows the honeycomb to be stowed collapsed until needed during an emergency. Evaluation of the DEA began with material characterization of the Kevlar-129 fabric/epoxy and ended with a full-scale crash test of a retrofitted MD-500 helicopter. During each evaluation phase, finite-element (FE) models of the test articles were developed, and simulations were performed using the dynamic FE code LS-DYNA. This paper focuses on simulations of two full-scale impact tests involving the DEA: a mass simulator and a DEA-retrofitted MD-500 helicopter. Isotropic (Mat 24) and composite (Mat 58) material models that were assigned to DEA shell elements were compared. Based on simulation results, the Mat 58 model showed better agreement with the test results. [ABSTRACT FROM AUTHOR]

The finite-element methodology is presented to evaluate the energy absorption performance of staggered triangular honeycombs under in-plane crushing loadings at impact velocities of 50-300 m/s. The minimum dynamic cushioning coefficient is proposed to characterize the maximum energy absorption efficiency of staggered triangular honeycombs. When all configuration parameters are constant, the energy absorption per unit volume is proportional to the square of the impact velocity; for a given impact velocity, the energy absorption per unit volume is related to the ratio of the cell wall thickness to the edge length by a power law and to the expanding angle by complicated analytical equations. The maximum energy absorption efficiency is insensitive to the impact velocity. Only for the smaller ratio of the cell wall thickness to the edge length does the maximum energy absorption efficiency increase with the increasing expanding angle. At a given impact velocity there is a threshold ratio of the cell wall thickness to the edge length. The maximum energy absorption efficiency decreases abruptly when the ratio is larger than the threshold. The threshold ratio is approximately equal to 0.04. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) materials possess inherently high strength-to-weight ratios, but their effective elastic moduli are low relative to civil engineering (CE) construction materials. While elastic modulus may be comparable to that of some CE materials, the lower shear modulus adversely affects stiffness. As a result, serviceability issues are what govern GFRP deck design in the CE bridge industry. An innovative solution to increase the stiffness of a commercial GFRP reinforced-sinusoidal honeycomb sandwich panel was proposed; this solution would completely replace the GFRP honeycomb core with a hexagonal honeycomb core constructed from commercial steel roof decking. The purpose of this study was to perform small-scale tests to characterize the steel hexagonal honeycomb core equivalent elastic moduli in an effort to simplify the modeling of the core. The steel core equivalent moduli experimental results were compared with theoretical hexagonal honeycomb elastic modulus equations from the literature, demonstrating the applicability of the theoretical equations to the steel honeycomb core. Core equivalent elastic modulus equations were then proposed to model and characterize the steel hexagonal honeycomb as applicable to sandwich panel design. The equivalent honeycomb core will enable an efficient sandwich panel stiffness design technique, both for structural analysis methods (i.e., hand calculations) and finite-element analysis procedures. [ABSTRACT FROM AUTHOR]

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models) and computational methods (finite-element, finite-difference, and mesh-free methods) used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys) are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures. [ABSTRACT FROM AUTHOR]

Both the crushing and indentation behaviors of sandwich materials are important aspects in failure analysis and energy absorption. In this paper, the core crushing strength of honeycomb materials from the experiment is briefly introduced, and the indentation of sandwich structures is studied in detail. Using the beam on elastic-plastic foundation models, theoretical formulations for predicting indentation behavior of sandwich materials are proposed, from which the mechanical response of elastic-plastic sandwich beams are obtained. Three stages of failure are clearly depicted by the global stiffness changes in the load versus displacement curve of elastic-plastic beams. The models are compared with the available experimental data and numerical simulation, and relatively close agreements are achieved. The compliance and compliance gradient derived form the indentation models are then incorporated with the equation of motion of the projectile to study impact response of elastic-plastic beams, and the impact energy dissipation due to the plasticity of elastic-plastic sandwich beam is uniquely recovered from the derived damping ratio. The beam on elastic-plastic foundation models proposed can be used to predict the indentation behavior of honeycomb sandwich materials, and the unique incorporation of the compliance and compliance gradient of the elastic-plastic sandwich beams in the standard mass-spring model can be utilized to characterize the effect of core compression and plasticity in the impact process. [ABSTRACT FROM AUTHOR]

Honeycomb structures have been used in different engineering fields. In civil engineering, honeycomb fiber-reinforced polymer (FRP) structures have been used as bridge decks to rehabilitate highway bridges in the United States. In this work, a simplified finite-element modeling technique for honeycomb FRP bridge decks is presented. The motivation is the combination of the complex geometry of honeycomb FRP decks and computational limits, which may prevent modeling of these decks in detail. The results from static and modal analyses indicate that the proposed modeling technique provides a viable tool for modeling the complex geometry of honeycomb FRP bridge decks. The modeling of other bridge components (e.g., steel girders, steel guardrails, deck-to-girder connections, and pier supports) is also presented in this work. [ABSTRACT FROM AUTHOR]

This paper presents a parametric study aimed at uncovering general design principles that govern the structural performance of honeycomb-type rigidified inflatable structures (RIS) as load-bearing wall systems for use in residential housing. This study involves the use of finite element modeling and optimization. A series of honeycomb-type RIS wall systems, each comprising different honeycomb cell sizes, are examined. The problem at hand is stated in the form of minimizing material volume subject to: permissible stress, maximum allowable deflection, and membrane thickness. The optimization results help identify optimal design configurations for given sets of loading conditions and material properties. The effects of various design parameters, such as cell size, material properties, and membrane thicknesses, are discussed. The performance of honeycomb-type RIS wall systems is compared with that of rectilinear-type RIS wall systems, which were studied previously. The work presented makes a significant step in establishing the feasibility of RIS for housing applications. [ABSTRACT FROM AUTHOR]

This paper examines several available analytic and experimental methods to determine the orthotropic material properties of honeycomb. Fifteen published sets of simple equations for the material properties were reviewed and their values calculated for a specific honeycomb aluminum core. The same core was tested with ASTM standard methods and the agreement between the theoretical material properties and the experimental results was considered. To reduce the time and cost for the experimental determination, a simple technique for measuring the main dynamic material properties of honeycomb is introduced. A good agreement was found between the major theoretical out-of-plane material properties of honeycomb, the experimental ASTM methods, and the presented dynamic approach. [ABSTRACT FROM AUTHOR]

Lightweight and heavy-duty fiber-reinforced polymer (FRP) composite honeycomb sandwich structures have been increasingly used in civil infrastructure. Unique cellular core configurations, such as sinusoidal core, have been applied in sandwich construction. Due to specific core geometry, the solutions for core effective stiffness properties are not readily available. This paper presents a mechanics of materials approach to evaluate the effective stiffness properties of sinusoidal cores. In particular, the internal forces of a curved wall in a unit cell are expressed in terms of resultant forces, and based on the energy method and principle of equivalence analysis, the in-plane stiffness properties of sinusoidal cores are derived. Both finite-element modeling and experimental testing are carried out to verify the accuracy of the proposed analytical formulation. To illustrate the present analytical approach as an efficient tool in optimal analysis and size selection of sinusoidal cores, several design plots are provided and discussed. The simplified analysis and formulation presented for sinusoidal cores can be used in design application of FRP honeycomb sandwich and optimization of efficient cellular core structures. [ABSTRACT FROM AUTHOR]

The World Trade Center collapse has brought attention to progressive collapse of tall buildings and the study of possible countermeasures. From the viewpoint of energy transfer, this analysis explains why the collapse could not stop by itself once began. By introducing a design parameter called collapse stability index that controls design against progressive collapse, it is found that conventional design of a tall building usually leads to an inherently unstable structure in the event of a progressive collapse. In a subsequent feasibility study in this paper, a heavy-duty metal-based honeycomb energy absorbing structure is proposed. Using a finite element analysis, it is demonstrated that the structure is capable of absorbing potential energy released in a tall building collapse. The added energy absorbing devices will only occupy a small percentage of the total floor space. By properly designing and installing such devices, a progressive collapse, should it happen in a tall building, may be arrested within a few floors, and hence, the building is inherently stable to the progressive collapse. The theory is also elaborated with the example of the World Trade Center collapse. [ABSTRACT FROM AUTHOR]

The wave propagation in sandwich plate rows with cellular core is analyzed and controlled. Honeycomb core materials of different geometry placed periodically along the structure introduce the proper impedance mismatch necessary to obstruct the propagation of waves over specified frequency bands (stop bands). The location and the extension of the stop bands can be optimized by proper selection of the geometrical and physical properties of the core. An optimal configuration of the core can be identified to design passive sandwich structures, which are stable and quiet over desired frequency bands. A theoretical model is developed to describe the wave propagation characteristics and the vibrations of a three-layered sandwich plate simply supported along its longitudinal edges. The core properties of the plate change periodically along the plate length. The wave propagation characteristics are estimated by analyzing the transfer matrix of each cell of the resulting periodic structure. The transfer matrix is also properly recast to obtain the cell’s dynamic stiffness matrix and to formulate a spectral finite element model for the periodic sandwich plate. The spectral finite element model allows predicting the dynamic behavior of the structure with a significantly reduced number of elements as compared to conventional finite elements. The numerical model is used to predict the dynamic response of the considered class of plates and to study their propagation and attenuation characteristics for various core configurations. The presented numerical results demonstrate the simplicity and the effectiveness of the proposed treatment, which reduces the transmission of waves and the plate vibrations over specified frequency bands without the need of additional passive or active control devices. Such unique characteristics can be employed to design lightweight composite panels behaving as mechanical filters. The filtering capabilities of such passive composite panels can be properly modified and optimized to fit required transmissibility levels over desired frequencies without compromising the size and the weight of the structure. [ABSTRACT FROM AUTHOR]

Polymer matrix composite (PMC)-infill walls hold great promise for energy dissipation when used in retrofitting applications where seismic activity is a consideration. This paper presents the analysis, design, and testing of PMC-infill walls developed for seismic retrofitting applications. The PMC-infill wall system consists of two fiber-reinforced polymer laminates with an infill of vinyl sheet foam. At the interface between the laminates, viscoelastic honeycomb is used to dissipate energy and improve the damping characteristics of the structure. As part of this research, analytical and experimental studies were performed to explore the effectiveness of this seismic retrofitting strategy and to examine the behavior of the PMC-infill wall system when subjected to monotonic and cyclic loading. A steel frame retrofitted with a PMC-infill wall was monitored to assess the resultant enhancements to its seismic-energy resistance capacity. In testing the PMC-infill wall system in this research, a large-scale steel frame was used to avoid the typical uncertainties associated with scaling the dimensions. The optimal design for the stacking sequence of a PMC-infill wall panel was determined based on the performance and material cost using the finite-element analysis. Finally, the observed behavior of the PMC-infilled frame was assessed on the bases of stiffness, strength, modes of failure, and energy dissipation output. The experimental and analytical studies demonstrate that the introduction of a PMC-infill wall panel in a semirigidly connected steel frame produces significant enhancements to stiffness, strength, and energy dissipation. [ABSTRACT FROM AUTHOR]

Focuses on a study that investigated the transverse shear stiffness of a honeycomb core, and developed a two-scale homogenization method for obtaining formulas for general configurations of thin-walled honeycomb structures. Background on the applications of sandwich structures with honeycomb core geometrics; Methodology; Results and discussion.

Provides information on a study which examined the crushing response of a polycarbonate circular cell honeycomb to inplane biaxial loading under displacement control. Details on the experiments; Results of the study; Discussion of findings.

An introduction to a special section of the journal is presented wherein the editors discuss various articles published within the issue on topics including an externally deployable composite honeycomb, the impact of the proposed Orion manned space capsule onto various types of sand, and ballistic tests on aluminum and titanium flat panel specimens.